1. Field of the Invention
The present invention relates to a plasma surface treating method and an apparatus therefor both utilizable for the formation of an oxide on a surface of a metal or a semiconductor at a high processing speed and also for the removal of a photoresist remaining on the surface during the course of a fine patterning process at a high processing speed, and wherein the extent to which the plasma surface treatment has progressed can be detected easily.
2. Description of the Prior Art
Some of the prior art plasma surface treating apparatuses will be discussed with reference to FIGS. 1 and 2.
Referring first to FIG. 1, reference numeral 1 represents a vacuum vessel; reference numeral 2 represents a first electrode which serves as an anode; reference numeral 3 represents a sample to be treated; reference numeral 4 represents a second electrode which serves as a cathode; reference numeral 5 represents a source of direct electric current; and reference numeral 6 represents a high frequency oscillator.
In the prior art plasma surface treating apparatus of a construction shown in FIG. 1, a high frequency generated from the high frequency oscillator 6 is applied to a gaseous medium introduced into the vacuum vessel 1 to generate a plasma inside the vacuum vessel 1.
Active species contained in the plasma generated in the vicinity of the high frequency oscillator 6 reach a surface of the sample 3 by an action of an electric field, developed between the first electrode 2 serving as the anode and the second electrode serving as the cathode, thereby to accomplish a surface treatment of the sample 3.
When the active species obtained are positive ions, the sample 3 to be treated is placed on the second electrode 4. In contrast, when the active species obtained are negative ions, the sample 3 to be treated is placed on the first electrode 2.
The voltage applied across the first electrode or anode 2 and the second electrode or cathode 4 should not be too high in order for the high frequency oscillator 6 to produce the plasma in stabilized fashion. In view of this, the prior art plasma surface treating apparatus generally employs some tens volts to be applied across the first electrode 2 and the second electrode 4 and is so designed as to form the electric field sufficient to guide the active species in the plasma towards the sample by the application of this voltage.
However, the prior art plasma surface treating apparatus discussed above is unable to provide a relatively high plasma current density and, accordingly, requires a long time to complete the surface treatment. Also, the prior art plasma surface treating apparatus requires the use of the high frequency oscillator 6 for the generation of the plasma, rendering the apparatus as a whole to be complicated in structure and expensive to manufacture.
The other prior art plasma surface treating apparatus shown in FIG. 2 comprises a vacuum vessel 1, a sample 3 to be treated, a source of direct electric current 5, and a cathode 7. In this prior art plasma surface treating apparatus, the vacuum vessel 1 confronting the cathode 7 serves as an anode and, therefore, when a voltage is applied to the anode (i.e., the vacuum vessel 1) and the cathode 7, a glow discharge is effected in a normal glow-discharge region between the anode 1 and the cathode 7, thereby to transform a gaseous medium in this normal glow-discharge region into a plasma.
However, in this prior art plasma surface treating apparatus, regardless of whether the active species in the plasma are positive ions or whether the active species in the plasma are negative ions, a gradient of increase in electric potential between the anode (i.e., the vacuum vessel 1) and the cathode 7 is steep in the vicinity of the cathode 7 and moderate in the vicinity of the anode as shown in a graph of FIG. 3.
Accordingly, the plasma surface treating apparatus as shown in FIG. 2 is applicable only where the principle active species are positive ions. In other words, where the principle active species are positive ions, the active species are drawn towards the sample by the steep gradient of increase in electric potential observable in the vicinity of the cathode and subsequently impinge upon the surface of the sample 3 to accomplish the surface treatment. However, where the principle active species are negative ions, most of the active species will only drift in the vicinity of the anode. Accordingly, the frequency of impingement of the active species upon the sample 3 is very low, thereby failing to accomplish a satisfactory surface treatment of the sample and, if not impossible, accomplishing the surface treatment at an extremely low processing speed. This is because the gradient of increase in electric potential observable in the vicinity of the anode is substantially flat.
Summarizing the foregoing, the prior art plasma surface treating apparatus of the construction shown in FIG. 1 has problems in that the processing speed is low and in that the use of the high frequency oscillator is essential enough to render the apparatus as a whole to be complicated in structure and expensive to manufacture. On the other hand, the prior art plasma surface treating apparatus of the construction shown in FIG. 2 has a problem in that, although simple in structure as compared with the plasma surface treating apparatus of FIG. 1, the apparatus itself cannot be used where the principle active species are negative ions.
Also, in any one of the prior art plasma surface treating apparatuses, it has been found difficult to comprehend the progress of plasma surface treatment taking place.